Nanocrystalline silicon carbide ͑SiC͒ thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T d) ranging from 80 to 575°C and different gas flow ratios ͑GFRs͒. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T d , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ͑HRTEM͒, micro-Raman, Fourier transform infrared ͑FTIR͒ and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300°C. The degree of crystallization increases with increasing T d and the crystalline fraction (f c) is 65%Ϯ2.2% at 575°C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ͑n͒ with T d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H 2 have large band gap (E g) and these values vary from 2.6 to 4.47 eV as T d is increased from 80 to 575°C. The size dependent shift in the E g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films.

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Alkaline earth metal and rare earth tungstate and molybdate compounds are promising candidates as host materials for high efficiency narrow spectral emission red phosphors when activated by trivalent europium (Eu3+). These phosphors emit in the range of 610–620 nm with a full width at half maximum (FWHM) of less than 10 nm, which makes them suitable for use in high color rendering index phosphor-converted white light emitting diodes (pc-WLEDs). However these phosphors suffer from poor excitation using the currently available GaInN based high efficiency blue LEDs in the 400–470 nm range. This paper discusses the role of various crystallographic structures on the excitation characteristics of the phosphor. Using appropriate crystal structures, it has been shown that Mo6+-O2− charge transfer band edge shifts from far-UV (280–350 nm) to near-UV and Blue (380–430 nm) region as the coordination number of the transition metal ion is increased from 4 to 6 making these phosphors suitable for excitation with near-UV or Blue LEDs. Furthermore it has been demonstrated that phosphors crystallized from flux exhibit significantly higher emission intensity compared to powders of the same composition synthesized using solid state reactions.

The response to ultraviolet illumination of ZnO nanoparticles deposited on LiNbO3 substrate was investigated using surface acoustic waves (SAWs) in the wide range of UV wavelengths from 280 to 375 nm. Deposition of ZnO nanoparticles caused a SAW transmission loss of 27 dB at 64 MHz due to the acoustoelectric attenuation. Acoustoelectric change in the SAW velocity by 3.78×10−4 under 375 nm illumination led to downshift in transmitted SAW phase by 5.5° at UV power density of 691 μW/cm2. The spectral measurements show the peak response at 345 nm with corresponding sensitivity on the order of 2.8 ppm/(μW/cm2).

We report femtosecond optically excited terahertz ͑THz͒ emission from tellurium doped GaSb at room temperature. The influence of the majority and minority carrier type and concentrations on the strength of the THz emission is investigated. Strong enhancement of THz emission in GaSb is observed as a result of compensation of native acceptors by tellurium donors. Surface field acceleration and the photo-Dember effect are identified as THz emission mechanisms in GaSb and modeled in dependence of the majority and minority carrier type and concentrations in our GaSb samples. THz emission from p-type GaSb is dominated by the photo-Dember effect whereas THz emission from n-type GaSb is dominated by surface field acceleration. The doping conditions under which THz emission is maximized are identified.